Methods of fabricating shims for joining parts

ABSTRACT

Methods of fabricating shims for joining parts are disclosed. An example method of fabricating shims for joining parts, wherein the parts having mating surfaces separated by a gap, includes: generating first digital data representing a first surface profile of a first part; generating second digital data representing a second surface profile of a second part to mate with the first part; determining distances between the first and second parts, as assembled, at multiple locations; generating a digital volume that closely matches a gap between the first and second parts based on the determined distances; generating a three dimensional digital representation of a shim to fill the gap using the first and second digital data; and automatically fabricating the shim matching the gap using a computer-controlled machine, the machine being controlled using the three dimensional digital representation of the shim.

RELATED APPLICATIONS

This patent arises from a continuation of U.S. patent application Ser.No. 13/156,101, filed Jun. 8, 2011. The entirety of U.S. patentapplication Ser. No. 13/156,101 is incorporated by reference herein.

TECHNICAL FIELD

The present disclosure generally relates to techniques for fitting andassembling parts together within desired tolerances, and deals moreparticularly with a method of designing and fabricating shims used tofill gaps between part interfaces.

BACKGROUND

The parts of an assembly are sometimes required to be joined togetherwith an accuracy that is within a preselected tolerance. For example, inthe aerospace industry, some parts may be required to be assembledtogether with less than a 0.005 inch gap between them. When the gapexceeds the preselected tolerance, a shim or similar filler may beinserted into the gap in order to assure a within tolerance fit betweenthe parts. The process of assembling and fitting parts together with therequired accuracy may become more challenging when the assembly processmust be carried out within confined spaces.

Several known methods have been used for measuring and filling part gapsduring the assembly process. According to one method, a set of feelergauges is used in a progressive trial-and-error process to measure thegap between two interfacing part surfaces. This approach is both timeconsuming and its accuracy may be dependent on the skill of thetechnician making the measurements. Using the manual gap measurements, acustom shim is constructed either manually or using automated machinetool processes.

A second method of measuring and fitting gaps between parts relies onmanual probing of the gap using an electronic feeler gauge. Electronicfeeler gauges may be difficult to use and the measurement results mayalso be dependent on the skill of the technician who carries out themeasurements.

A third method of measuring and filling gaps between parts involvesfilling the gap with a plastic slurry material that cures in place toform a solid filler object. This solution to the problem may haveseveral disadvantages in some applications. For example, the plasticslurry material must remain frozen until just before use and must bebonded to one of the parts but not to the opposite part. The parts towhich the slurry material is to be bonded must be coated with a releaseagent in advance of application. In addition, the slurry material mayexert a hydraulic pressure on the parts during the application process,which may deform or displace the parts slightly, reducing assemblyaccuracy. Another disadvantage of the slurry material is that thematerial may shrink in a non-uniform manner during curing. Also, theapplication of the material is time critical, and material may requirean extended period in which to cure during which further work on theassembly may not be performed.

Still another method of filling the gaps between mating parts, sometimesreferred to as predictive shimming, involves scanning the interfacingpart surfaces in an attempt to predict the exact shape of the gap orvoid between these surfaces. The parts of the assembly are virtuallyfitted together and a shim is fabricated based on the virtuallypredicted relationship between the parts. The problem with thisapproach, however, is that the parts of the assembly, especially largeassemblies, may experience significant relative movement of the partsbetween the time the parts are initially scanned and the time ofassembly, resulting in changes of the shape and/or dimensions of thegap. Another disadvantage of this method lies in its dependence onrelatively high global accuracy of measurement and assembly.

SUMMARY

Disclosed example methods of fabricating shims for joining parts,wherein the parts having mating surfaces separated by a gap, comprise:generating first digital data representing a first surface profile of afirst part; generating second digital data representing a second surfaceprofile of a second part to mate with the first part; determiningdistances between the first and second parts, as assembled, at multiplelocations; generating a digital volume that closely matches a gapbetween the first and second parts based on the determined distances;generating a three dimensional digital representation of a shim to fillthe gap using the first and second digital data; and automaticallyfabricating the shim matching the gap using a computer-controlledmachine, the machine being controlled using the three dimensionaldigital representation of the shim.

Other disclosed example methods of fabricating shims for joining parts,wherein the parts have mating surfaces separated by a gap, comprise:generating first digital data representing a first surface profile of afirst part; generating second digital data representing a second surfaceprofile of a second part to mate with the first part; physicallyassembling the first and second parts into an assembly; placing anon-contact distance measurement device between the assembled first andsecond parts; measuring distances between the assembled first and secondparts at multiple locations; generating a digital volume thatsubstantially matches a gap between the first and second parts based onthe measured distances; disassembling the first and second parts;generating a three dimensional digital representation of a shim to fillthe gap by using the first and second digital data to map the first andsecond surface profiles onto the digital volume; automaticallyfabricating the shim matching the gap using a computer-controlledmachine, the machine being controlled using the three dimensionaldigital representation of the shim; physically reassembling the firstand second parts; and placing the fabricated shim between the parts tofill the gap.

Other features, benefits and advantages of the disclosed embodimentswill become apparent from the following description of embodiments, whenviewed in accordance with the attached drawings and appended claims.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

FIG. 1 is an illustration of a cross sectional view of an assembly oftwo parts having a gap therebetween.

FIG. 2 is an illustration of a cross sectional view of a shim forfilling the gap between the parts shown in FIG. 1.

FIG. 3 is an illustration similar to FIG. 1, but showing the shim ofFIG. 2 having been installed between the parts.

FIG. 4 is an illustration of a flow diagram broadly showing the steps ofa method of fabricating a shim according to the disclosed embodiments.

FIG. 5 is an illustration of a flow diagram showing additional detail ofthe method shown in FIG. 4.

FIG. 6 is an illustration of a cross sectional view of a part that joinsitself.

FIG. 7 is an illustration of a cross sectional view of two parts thatare joined to a third part using the disclosed method.

FIG. 8 is an illustration of a cross sectional view of two partsrequiring the use of multiple shims.

FIG. 9 is an illustration of a cross sectional view of a shim used tojoin together multiple parts.

FIG. 10 is an illustration of a cross sectional view of two curved partshaving substantially constant radii of curvature and having a curved gaptherebetween.

FIG. 11 is an illustration of two parts joined together by substantiallyorthogonal shims.

FIG. 12 is an illustration of a cross sectional view showing multipleparts having various part joining interfaces joined together byindividual shims.

FIG. 13 is an illustration showing details of several of the partinterfaces shown in FIG. 12.

FIG. 14 is an illustration of a cross sectional view showing multiplepart interfaces between trapped parts.

FIG. 15 is an illustration of a cross sectional view of a part whosethickness is being measured.

FIG. 16 is an illustration of a cross sectional view showing the part inFIG. 15 having been assembled with a second part, wherein a gap betweenthe two parts is being measured.

FIG. 17 is an illustration of gap measurements between a vertical tailstabilizer and the fuselage of an aircraft.

FIG. 18 is an illustration of a flow diagram of aircraft production andservice methodology.

FIG. 19 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring to FIG. 1, first and second parts 30, 32 are to be joinedtogether with a part fit-up that is within a desired tolerance. Theparts 30, 32 have opposing, interface surfaces 36, 38 respectively,which are to be joined together at a joining interface 35. Because theinterface surfaces 36, 38 may not perfectly join each other along theinterface 35, a gap or void 34 may be present between the part interfacesurfaces 36, 38.

In accordance with the disclosed embodiments, a method is provided ofproducing a shim 30 shown in FIG. 2 that is designed and manufactured tosubstantially completely fill the gap 34 between the parts 30, 32 at theinterface 35. As used herein the term “shim” is intended to include,without limitation, joining parts, fillers and other elements that areused to fill one or more gaps or voids between two or more parts beingassembled to achieve a fit of a prescribed tolerance. In someapplications, the shim 40 may comprise one of the parts of an assemblyof parts. In the present example, the shim 40 has an upper flat surface42 substantially matching surface 36 of part 30, while the lower surface34 of the shim 40 is contoured to match the contoured surface 38 of part32. As will become apparent later however, the surfaces of the shim 40that interface with the parts 30, 32 may have any shape or contour thatsubstantially matches that of the parts 30, 32.

FIG. 3 illustrates the shim 40 of FIG. 2 having been installed in thegap 34 so as to substantially completely fill the gap 34 and therebyjoin the two parts 30, 32 together at the joining interface 35.

It may be useful here to define several terms that used from time totime in the present description. The term “independent surface” is usedherein is intended to mean a digital surface that stands alone indefinition and is free from all constraints to other digital surfaces.“Semi-independent surface” refers to a digital surface that shares someconstraints with other surfaces that have been determined to havesufficient accuracy to meet prescribed tolerances. “Joining interface”as used herein, is intended to refer to a collection of two or moresurfaces on one or more parts that are to be joined into an assembly orpart by means of custom formation of one or more of the surfaces or bymeans of a shim or joining part. “Unconstrained datasets” refer to acollection of independent surfaces, points or other digital data thatwill be used to create a digital shim or a digital joining part.“Partially constrained datasets” refers to a collection ofsemi-independent surfaces, independent surfaces, points and/or otherdigital data that may be used to create a digital shim or digitaljoining part. “Digital joining part” refers to a part on which digitalsurfaces are defined such that they may contact themselves or otherparts in multiple places in a manner that each interface has a fit of aprescribed tolerance. “Shim” and “digital shim” refer to a digitaldefined shim or part that is composed of independent digital surfaces,points, or other digital data that has been related or constrained toone another to create the bounds of a volume to which a physical shimmay be manufactured.

Attention is now directed to FIG. 4 which broadly illustrates the stepsof a method of producing a shim 40 (FIG. 3) for fitting one or moreparts 30, 32 together according to the disclosed embodiments. Beginningat 46, the surface profile of the mating surfaces of two or more partsare determined. For example, the surface profiles of interface surfaces36, 38 of parts 30, 32 shown in FIG. 1 are determined. These surfaceprofiles may be determined using any of various techniques, such as bycalling up pre-existing 3-D CAD (computer aided design) design filesthat digitally define the surfaces 36, 38, or by digitally scanning thesurfaces 36, 38 either before or after the parts 30, 32 have beenassembled, using a laser scanner, computer controlled coordinatemeasuring machine or other suitable equipment (all not shown). Next, atstep 48 a three dimensional (3-D) digital volume is generated thatsubstantially matches the gap 34 between parts 30, 32 (see FIG. 1). Thedigital volume generated in step 48 establishes a basic inner volumedefinition of a shim object which would closely fill the gap 34. At step50, a 3-D digital representation of the shim 40 is generated by mappingthe part surface profiles obtained in step 46 onto the digital volumegenerated at step 48. The results of step 50 is a digital soliddefinition of a shim 30 which would substantially fill the gap 34. Atstep 52 the 3-D representation of the shim generated in step 50 is usedto fabricate the shim 40 using any of various process, such as, withoutlimitation, computer controlled machining.

Attention is now directed to FIG. 5 which illustrates additional detailsof an embodiment for carrying out the method shown in FIG. 4. Beginningat step 54, a first digital dataset is produced which defines eachjoining part surface such as surfaces 36, 38 of the parts 30, 32 shownin FIG. 2. The first digital dataset may be produced by digitallyscanning the interface surfaces 36, 38 using any of various techniques,including, for example and without limitation, a computer controlled CMM(coordinate measuring machine), laser scanner, etc. Alternatively,digital files representing the interface surfaces 36, 38 may be importedfrom an existing source, such as one or more CAD design files thatdefine the surfaces 36, 38 in 3-D.

At step 56, the parts 30, 32 are assembled on a best-fit basis. Thedataset produced in step 54 may be produced either before or after theparts 30, 32 are assembled in step 56. At step 58 a second digitaldataset is produced which defines the 3-D spatial relationship betweenthe part interface surfaces 36, 38. The second digital data set may beproduced using any of various techniques which establish the relativepositions of the interface surfaces 36, 38 in 3-D space. For example,following assembly of the parts 30, 32 in step 56, a laser scanner (notshown) may be inserted into the gap 34 and used to scan the surfaces 36,38. This scanning process generates digital data representing thedistance between the surfaces 36, 38 at a multitude of pointsrepresenting the digital volume matching the gap previously discussed inconnection with step 48 in FIG. 4.

Next, at 60, the parts 30, 32 may be disassembled, as required, althoughin some applications the parts 30, 32 may remain in their assembledstate until a shim 40 has been fabricated and inserted into the gap 34between the parts 30, 32. At step 62, automated data processingimplemented by a computer (not shown) may be used to produce a thirddata set that represents the shape and dimensions of the gap 34 to befilled. Step 62 is similar to step 50 shown in FIG. 4 in which a 3-Drepresentation of the shim 40 is generated corresponding to the shapeand dimensions of the gap 34. At step 64, a shim or similar custom partis fabricated using the third dataset produced at step 62. The shim 40may be fabricated, for example and without limitation, using CNCmachining. Finally, as shown in 66, the shim 40 may be inserted into thegap 34 between the assembled parts 30, 32, although if the parts 30, 32have been previously disassembled at step 60, then the parts 30, 32 arereassembled with the shim 40 inserted into the gap 34.

The disclosed method may be employed to assemble and fit a wide varietyof parts having differing shapes and interface surface contours. Forexample, the method may be used to assemble and fit parts havingparallel joining interfaces, constant radius of curvature joininginterfaces, orthogonal joining interfaces, and others (all not shown).Constraint relationships required to establish the relationship betweenjoining surfaces may be established using any of a variety oftechniques, including mechanically or electronically measuring thedistance between the joining surfaces at multiple locations on the partsurfaces 36, 38.

FIG. 6 illustrates a single part 65 having opposing portions 70, 72separated by a gap 68. The disclosed method may be used to fabricate ashim 74 that substantially matches the shape of the gap 68 and resultsin fitting of the two portions 70, 72 together within a desiredtolerance.

Referring to FIG. 7, the disclosed method may be employed to fabricate ajoining part 80 which joins two other parts 76, 78 together, wherein thejoining part 80 forms part of a part assembly 85. In this example, parts76 and 78 are joined along a joining interface 82 to which the joiningpart 80 conforms.

FIG. 8 illustrates an assembly of two parts 84, 86 representing apartially constrained dataset, and respectively having interfacesurfaces 90, 95. Part 84 includes grooves 92 that define sevensemi-independent interface surfaces 90, while part 86 has a singleindependent surface 95. In order to fit the interfacing and surfaces 90,95 within desired tolerances, the disclosed method may be employed tofabricate seven shims (not shown in FIG. 8) which are placed betweensurfaces 90, 95 to fill any gaps that may be present therebetween.

FIG. 9 illustrates a joining part 96 fabricated according to thedisclosed method that may be employed to join multiple other parts 94along differing interface surfaces 101. A groove 98 through part 94 aresults in part 94 a having two independent surfaces 100 a fitted to thejoining part 96, while the other parts 94 have only one independentsurface 101 fitted to the joining part 94.

FIG. 10 illustrates an assembly of parts 102, 104 which respectivelynear-constant radius of curvature interfacing surfaces 106, 107 areseparated by a gap 110. According to the disclosed method, a shim 111designed and fabricated by the disclosed method, has a suitablecurvature and dimensions which closely fill the gap 110.

FIG. 11 illustrates an assembly of parts 112, 114 that may be joinedtogether by substantially orthogonal shims 116, 118 designed andfabricated in accordance with the disclosed method.

FIG. 12 illustrates an assembly 115 of sixteen generally square parts120 fitted together by shims 122 produced in accordance with thedisclosed method. In this example, each of the parts 120 may haveregular or irregular interface surfaces 124 forming gaps 125 filled bysegmented shims 122. There may be no theoretical limit to the number ofparts 120 or the size of the overall assembly 115 that may be fittedusing the disclosed method using locally accurate shimming. Geometricchanges within the assembly 115 may usually occur over a broad area.According to the disclosed method, segmented shims 122 may be used thatare small enough that geometry changes in the assembly 115 due towarpage or the like do not shift the shims 122 out of tolerance.

FIG. 13 illustrates four generally square parts 130, similar to thoseshown in FIG. 12, which have generally parallel interface surfaces 138,140, 142, 144, 146, some of which however, may include uneven surfacecontours, e.g. 140, 146. The technique used to establish referencepoints at the interface surfaces 138-146 will vary depending upon thecomplexity of the contour of interface surface 138-146. For example, thepart interface shown at 132 comprises two complex contoured surfaces138, 140. In this case, both surfaces 138, 140 are referenced laterallywith respect to each other, and surface reference points on bothsurfaces 138, 140 are therefore used for gap measurement. One techniquefor accomplishing this referencing is to tie the two adjacent parts 130together using common features such as three common holes (not shown) inthe parts 130. Another technique would be to measure lateral differencesbetween reference features and the assembled parts as well as the gap135 between the surfaces 138, 140.

At the surface interface shown at 134, the opposing interface surfaces142 are generally smooth and parallel, consequently, in order toestablish the relationship between the opposing interface surfaces 142,gap measurements need only be measured at three points on either of thesurfaces 142. Finally, as shown at part 136, one of the interfacesurfaces 146 is relatively highly contoured, while the other opposinginterface surface 144 is relatively smooth. In this case, the referencepoints for gap measurement need be placed only on the contoured surface146.

FIG. 14 illustrates trapped joining interfaces 156, 158, 160 betweenmating parts 152, 154 that are trapped within a common base part 148.Thus, the two mating parts 152, 154 are constrained at both ends by thestack-up of the common part 148. In this example, it is desirable toproduce shims 150 a, 150 c and then perform the necessary measurementsand fabrication steps to produce the third shim 150 b.

As previously discussed, a variety of techniques can be employed toestablish the relationship between two parts 30, 32 (FIG. 1) for thepurposes of calculating a solid volume that will fill a gap 34 betweenthe parts 30, 32. For example, FIGS. 15 and 16 illustrate a techniquefor measuring gaps between two parts 178, 186 (FIG. 16) which have oneor more holes 179. In this example, part 178 may comprise an aircraftskin 178 having one or more holes 179 at known locations formingreference points on the skin 178. As shown in FIG. 15, in order to firstdetermine the thickness 180 of the skin 178, the tip 184 of a depthprobe 182 is inserted into the hole 179 and is brought into contact witha backing disk 186, following which the thickness 180 of the skin 178may be measured. Then, as shown in FIG. 16, a second part 186 isassembled onto the skin 180, which may result in a gap 187 between theskin 178 and the part 186. The tip 184 of the depth probe 182 is thenreinserted into the hole 184 until it comes into contact with the part186, allowing a measurement of the distance “D” between the two parts178, 186 at the location of the hole 179. Using similar techniques, itmay be possible to measure gap distances between more than two stackedparts.

FIG. 17 illustrates the assembly of a vertical tail stabilizer 212 on afuselage 214 of an aircraft using the disclosed method. The verticalstabilizer 212 is brought into close proximity and held in positionimmediately above the fuselage 214. Three gap measurements are thenperformed at both the front 216 and the rear 218 of the assembly therebyestablishing the spatial relationship between the stabilizer 212 and thefuselage 214. Based upon these gap measurements which establish thespatial relationship between the stabilizer 212 and the fuselage 214 andthe surface profiles of these two parts, one or more suitable shims (notshown in FIG. 16) may be fabricated to achieve a fit between thestabilizer 212 and the fuselage 214 within desired tolerances.

Embodiments of the disclosure may find use in a variety of potentialapplications, particularly in the transportation industry, including forexample, aerospace, marine and automotive applications. Thus, referringnow to FIGS. 18 and 19, embodiments of the disclosure may be used in thecontext of an aircraft manufacturing and service method 220 as shown inFIG. 18 and an aircraft 224 as shown in FIG. 19. Aircraft applicationsof the disclosed embodiments may include, for example, withoutlimitation, assembly and fitting fuselage skins, wings and wing skins,stiffeners, control surfaces, hatches, floor panels, door panels, accesspanels and empennages, to name a few. During pre-production, exemplarymethod 220 may include specification and design 226 of the aircraft 224and material procurement 228. During production, component andsubassembly manufacturing 230 and system integration 232 of the aircraft224 takes place. Thereafter, the aircraft 224 may go throughcertification and delivery 234 in order to be placed in service 236.While in service by a customer, the aircraft 224 is scheduled forroutine maintenance and service 238 (which may also includemodification, reconfiguration, refurbishment, and so on). During any ofstages 230, 232 and 238, shims produced according to the disclosedmethod may be used to join parts, components or assemblies of theaircraft 224.

Each of the processes of method 220 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 19, the aircraft 224 produced by exemplary method 220may include an airframe 240 with a plurality of systems 242 and aninterior 244. Examples of high-level systems 242 include one or more ofa propulsion system 248, an electrical system 248, a hydraulic system250, and an environmental system 252. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosure may be applied to other industries, such as the marine andautomotive industries. The disclosed embodiments may be used to produceshims 241 that are employed to fit and join various parts, componentsand subassemblies of the airframe 240.

Systems and methods embodied herein may be employed during any one ormore of the stages of the production and service method 220. Forexample, components or subassemblies corresponding to production process230 may be fabricated or manufactured in a manner similar to componentsor subassemblies produced while the aircraft 224 is in service. Also,one or more apparatus embodiments, method embodiments, or a combinationthereof may be utilized during the production stages 230 and 232, forexample, by substantially expediting assembly of or reducing the cost ofan aircraft 224. Similarly, one or more of apparatus embodiments, methodembodiments, or a combination thereof may be utilized while the aircraft224 is in service, for example and without limitation, to maintenanceand service 238.

Although the embodiments of this disclosure have been described withrespect to certain exemplary embodiments, it is to be understood thatthe specific embodiments are for purposes of illustration and notlimitation, as other variations will occur to those of skill in the art.

What is claimed is:
 1. A method of fabricating shims for joining parts,wherein the parts having mating surfaces separated by a gap, comprising:generating first digital data representing a first surface profile of afirst part; generating second digital data representing a second surfaceprofile of a second part to mate with the first part; determiningdistances between the first and second parts, as assembled, at multiplelocations; generating a digital volume that closely matches a gapbetween the first and second parts based on the determined distances;generating a three dimensional digital representation of a shim to fillthe gap using the first and second digital data; and automaticallyfabricating the shim matching the gap using a computer-controlledmachine, the machine being controlled using the three dimensionaldigital representation of the shim.
 2. A method as defined in claim 1,wherein determining the distances between the first and second parts asassembled comprises determining the distances between the first andsecond parts when the first and second parts are physically assembled.3. A method as defined in claim 1, wherein generating the threedimensional digital representation of the shim comprises mapping thefirst and second surface profiles onto the digital volume.
 4. A methodas defined in claim 1, wherein generating the first digital datacomprises digitally scanning surfaces of the first part.
 5. A method asdefined in claim 4, wherein generating the second digital data comprisesdigitally scanning surfaces of the second part.
 6. A method as definedin claim 4, wherein digitally scanning surfaces of the first partcomprises using a laser scanner.
 7. A method as defined in claim 1,wherein automatically fabricating the shim comprises usingcomputer-controlled machining.
 8. A method as defined in claim 1,wherein generating the digital volume comprises establishing relativepositions of a first interface surface having the first surface profileand a second interface surface having the second surface profile.
 9. Amethod as defined in claim 1, wherein the gap is defined by three ormore parts including the first and second parts, and generating thedigital volume comprises determining contours of the digital volumedefined by the three or more parts.
 10. A method as defined in claim 1,wherein generating the digital volume comprises using respective surfacereference points present on the first and second parts.
 11. A method offabricating shims for joining parts, wherein the parts have matingsurfaces separated by a gap, comprising: generating first digital datarepresenting a first surface profile of a first part; generating seconddigital data representing a second surface profile of a second part tomate with the first part; physically assembling the first and secondparts into an assembly; placing a non-contact distance measurementdevice between the assembled first and second parts; measuring distancesbetween the assembled first and second parts at multiple locations;generating a digital volume that substantially matches a gap between thefirst and second parts based on the measured distances; disassemblingthe first and second parts; generating a three dimensional digitalrepresentation of a shim to fill the gap by using the first and seconddigital data to map the first and second surface profiles onto thedigital volume; automatically fabricating the shim matching the gapusing a computer-controlled machine, the machine being controlled usingthe three dimensional digital representation of the shim; physicallyreassembling the first and second parts; and placing the fabricated shimbetween the parts to fill the gap.
 12. A method as defined in claim 11,wherein measuring the distances between the assembled first and secondparts is performed at at least three points.
 13. A method as defined inclaim 11, wherein measuring the distances between the assembled firstand second parts comprises using a computer-controlled coordinatemeasuring machine or a laser scanner.
 14. A method as defined in claim11, wherein automatically fabricating the shim comprises usingcomputer-controlled machining.
 15. A method as defined in claim 11,wherein physically assembling the first and second parts into theassembly comprises assembling the first and second parts on a best-fitbasis.
 16. A method as defined in claim 11, wherein generating the firstdigital data comprises digitally scanning surfaces of the first part.17. A method as defined in claim 16, wherein generating the seconddigital data comprises digitally scanning surfaces of the second part.18. A method as defined in claim 16, wherein digitally scanning surfacesof the first part comprises using a laser scanner.
 19. A method asdefined in claim 11, wherein generating the first digital data comprisesloading first computer aided design data that defines surfaces of thefirst part.
 20. A method as defined in claim 19, wherein generating thesecond digital data comprises loading second computer aided design datathat defines surfaces of the second part.